import java.util.*;
public class MethodExp3 {
static double circleArea(double radiusIn){
	double sIn;
	final double Pi = 3.14;
	sIn = radiusIn*radiusIn*Pi;
	return sIn;
}  

	public static void main(String[] args) 
	{
		Scanner sc = new Scanner(System.in);
		double radius;
		radius = sc.nextDouble();
		double area = circleArea(radius);
		System.out.println(area);
	}
}
